FCP 7 will not launch

Hello All,
My system has been running fine. I have FCP X and FCS 3.0 installed. I use both tcp x and tcp 7.0.3.
For some reason, FCP 7 will no longer launch. I have tried:
deleting preferences, and re-installing, and copying working app from backup disk.
All to no avail. If I boot off the backup disk - FCP 7 launches fine!

I have tried reformatting the hard disk, and copying from my backup disk using Carbon Copy Cloner.
The clone boots fine, and I can launch FCP 7 from it.

Any ideas here? I do not want to reformat, and then reload everything from scratch.
Should I try a different disk??